1. Field of the Invention
This invention relates to a capacitive multikey keyboard for inputting data into a computer. More specifically, the invention relates to an array or matrix keyboard potentially involving a large number of individual keys wherein the specific row and column of the key being pressed is identified by the computer by virtue of measuring the capacitance of a row and column determining keyboard output circuits.
2. Description of the Prior Art
Multikey keyboards for inputting data into a computer generally involve a plurality of normally open switches wherein the pressing of each key of the keyboard closes a corresponding switch. The set of normally open switches can be viewed as defining a switch matrix or switch array which in the conventional prior art keyboards have a plurality of input lines and a plurality of output lines. Pressing a key on the keyboard thus closing the corresponding switch creates electrical continuity and completes the circuit between the specific input and output lines corresponding to the respective position or identity of the key being pressed. This plurality of keyboard leads, in the conventional keyboard, is connected to at least one encoder which translates or converts the signals from the multiple key input circuits into a single alphanumeric coded output signal; e.g. into ASCII or binary coded decimal (BCD) format or the equivalent. The output signal from the keyboard encoder can then either be directed to the computer as the keyboard input or can be further processed by additional dedicated keyboard circuitry, depending on the particular manufacturing and overall computer system requirements, before entering the computer. Thus, it is not uncommon to find that the keyboard in addition to having an encoder will have its own dedicated memory and logic circuit essentially duplicating, in principle, that which the central processing unit (CPU) is theoretically capable of doing and consequently, increasing the cost of the keyboard. In practice, the presence of multiple input and output lines from the keyboard to the encoder tends to limit the number of keys present on the keyboard. Thus, in principle, the need for a relatively inexpensive, yet reliable, keyboard having the ability to contain a vast number or array of keys, yet having only a few output lines that bypass the encoder and optional auxiliary circuitry to serve as direct analog input to the computer still exists and represents a desirable theoretical objective.